1. Field of the Invention
The present invention relates to an electrode of an electric device, and more particularly to improvements in the conductive components included in the electrode.
2. Technical Background
Methods are widely known wherein a conductive paste is used as the raw material of an electrode. Micronization of electrode patterns has advanced together with the functional improvements in electronic devices, and photosensitive paste is used to form fine lines thereon. For example, a fine electrode pattern is used to improve the resolution of a plasma display panel (PDP).
The composition of the photosensitive paste generally includes a monomer in addition to a photopolymerization initiator, a conductive component, glass frit, organic binder, and solvent. The applied photosensitive paste is exposed through a mask, and polymerization of the monomer proceeds at the exposed locations. Thereafter, development and firing are carried out, and an electrode consisting of a conductive component and glass as a binder is formed thereby.
Silver is generally used as the conductive component (e.g., U.S. Pat. No. 5,047,313 and US Patent 20050287472). Capital investment for the furnace can be decreased because precious metals such as gold, silver, and palladium can be fired in air. Using precious metals, however, invites a sharp rise in material costs because precious metals are expensive.
Copper is widely used as a conductive component in semiconductor circuits and the like. Copper has the advantage of being less expensive than silver. However, copper cannot be fired in air because it oxidizes easily, and this increases capital investment because firing under a nitrogen atmosphere and the like is required.
A method using boron together with metal powder has been disclosed as technology that enables air firing of an easily oxidizable metal in a non-photosensitive paste (U.S. Pat. No. 4,122,232). In the examples of U.S. Pat. No. 4,122,232, copper powder finer than 325 mesh is used. The average particle size of the copper powder is not specifically described, but the average particle size of copper powder sorted using a 325 mesh is generally 40 to 50 μm.
Various technical obstacles have emerged, however, when this technology was applied to photosensitive paste. More specifically, boron scatters light, and there has been a problem because the exposed light is scattered when boron is added to the photosensitive paste, and the shape of the pattern is adversely affected thereby. Moreover, a small particle size is preferred in the conductive component to obtain an excellent fine line configuration, but when the particle size of the conductive component is small, the surface area thereof increases and as a result, oxidation proceeds more easily. It is preferable to increase the amount of added boron to inhibit the progress of oxidation, but if a large amount of boron is contained therein, the resistance of the electrode increases because boron has poor conductivity.
Thus, in the process of forming an electrode using a paste, the development of technology is needed that will satisfy the following requirements of: 1) enabling the use of inexpensive copper powder, 2) enabling firing to be performed in air, 3) enabling a fine pattern to be formed, and 4) enabling low electrode resistance.